Composite structures having improved heat aging and interlayer bond strength

ABSTRACT

Disclosed herein are composite structures having improved heat aging, processes for making them, and end use articles. The composite structures comprise a polyamide matrix resin composition comprising a matrix heat stabilizer ; a fibrous material and a polyamide surface resin composition comprising copper based heat stabilizer; wherein: the matrix heat stabilizer is different than the copper based heat stabilizer; and wherein the fibrous material is impregnated with the polyamide matrix resin composition.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 61/408,166, filed Oct. 29, 2010, which is now pending,the entire disclosure of which is incorporated herein by reference; andU.S. Provisional Application Nos. 61/410,093, filed Nov. 4, 2010;61/410,100, filed Nov. 4, 2010; 61/410,104, filed Nov. 4, 2010; and61/410,108, filed Nov. 4, 2010; all of which are now pending, the entiredisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of composite structureshaving improved heat aging, processes for making them, and end usearticles.

BACKGROUND OF THE INVENTION

With the aim of replacing metal parts for weight saving and costreduction while having comparable or superior mechanical performance,structures based on composite materials comprising a polymer matrixcontaining a fibrous material have been developed. With this growinginterest, fiber reinforced plastic composite structures have beendesigned because of their excellent physical properties resulting fromthe combination of the fibrous material and the polymer matrix and areused in various end-use applications. Manufacturing techniques have beendeveloped for improving the impregnation of the fibrous material with apolymer matrix to optimize the properties of the composite structure.

In highly demanding applications, such as for example structural partsin automotive and aerospace applications, composite materials aredesired due to a unique combination of light weight, high strength andtemperature resistance.

High performance composite structures can be obtained usingthermosetting resins or thermoplastic resins as the polymer matrix.Thermoplastic-based composite structures present several advantages overthermoset-based composite structures including the ability to bepost-formed or reprocessed by the application of heat and pressure.Additionally, less time is needed to make the composite structuresbecause no curing step is required and they have increased potential forrecycling.

Among thermoplastic resins, polyamides are particularly well suited formanufacturing composite structures. Thermoplastic polyamide compositionsare desirable for use in a wide range of applications including partsused in automobiles, electrical/electronic parts, household appliancesand furniture because of their good mechanical properties, heatresistance, impact and chemical resistance and because they may beconveniently and flexibly molded into a variety of articles of varyingdegrees of complexity and intricacy.

With the aim of improving the manufacturing process for making compositestructures and integrated composite structures and allowing an easier,shorter and uniform mixing or impregnation of fibrous materials, severalways have been developed to decrease the melt viscosity of the polymermatrix. By having a low melt viscosity, polymer compositions flow fasterand are thus easier to process. By reducing the melt viscosity of thepolymer matrix, the time needed to reach the desired degree of mixingmay be shortened, thereby increasing the overall manufacturing speed andthus leading to increased productivity.

However, the use of a low melt viscosity polyamide composition forimproving or accelerating the mixing or impregnation of fibrousmaterials may lead to composite structures that are not ideal for highlydemanding applications such as the automotive field due to inferiormechanical and heat aging properties.

The addition of heat stabilizers to polymer matrix compositions canallow for a higher impregnation temperature which lowers the viscosityof the polymer matrix composition but these heat stabilizers can alsointerfere with adhesion of the overmolding resin.

U.S. Pat. No. 7,763,674 discloses a fiber reinforced polyamidecomposition heat stabilized with a copper iodide/potassium iodidemixture.

US 2010/0120959 discloses polyamide compositions comprising a transitionmetal ion-modified clay as a heat-stabilizer. The metal ion for use inmodifying the clay is a transition metal selected from the transitionmetals in Group IB, VIIB, VIIB and VIII of the Periodic Table andcombinations thereof.

US 2009/0269532 teaches a multilayer structure comprising at least onestabilized layer. The stabilized layer is stabilized with 0.5%stabilizer based on copper iodide and potassium iodide. This stabilizeris constituted of 10% copper iodide, 80% potassium iodide and 10% zincstearate.

US 2008/0146718 discloses a non-fibrous-reinforced thermoplastic moldingcomposition comprising a metal powder as a heat stabilizer wherein themetal powder has a weight average particle size of at most 1 mm and themetal in the metal powder is selected from the group consisting ofelementary metals from Group VB, VIIB, VIIB and VIIIB of the PeriodicTable, and mixtures thereof.

U.S. Pat. No. 7,811,671 discloses films which comprise polyamidecompositions which use potassium iodide and cuprous iodide with amagnesium stearate binder as a heat stabilizer.

FR 2,158,422 discloses a composite structure made of a low molecularweight polyamide matrix and reinforcing fibers. Due to the low molecularweight of the polyamide, the polyamide has low viscosity. The lowviscosity of the polyamide matrix allows an efficient impregnation ofthe reinforcing fibers.

U.S. Pat. No. 7,323,241 discloses a composite structure made ofreinforcing fibers and a branched polyamide resin having a starstructure. The disclosed polyamide having a star structure is said toexhibit a high fluidity in the molten state thus making possible a goodimpregnation of the reinforcing fibers so as to form a compositestructure having good mechanical properties.

WO 2007/149300 discloses a semi-aromatic polyamide composite articlecomprising a component comprising a fiber-reinforced material comprisinga polyamide matrix composition, an overmolded component comprising apolyamide composition, and an optional tie layer there between, whereinat least one of the polyamide compositions is a semi-aromatic polyamidecomposition

However, there is still a need for a composite structure comprising amatrix resin composition that can rapidly and efficiently impregnate afibrous material and wherein the composite structure exhibits goodlong-term heat stability.

SUMMARY OF THE INVENTION

There is disclosed and claimed herein a composite structure comprising:

-   -   a polyamide matrix resin composition comprising        -   from 0.1 to at or about 3 weight percent of a matrix heat            stabilizer based on the weight of the polyamide matrix resin            composition;        -   a fibrous material selected from woven or non-woven            structures, felts, knits, braids, textiles, fibrous battings            or mats, and combinations of these; and        -   a polyamide surface resin composition comprising        -   0.1 to 3 weight percent of a copper based heat stabilizer            based on the weight of the polyamide surface resin            composition    -   wherein:    -   the matrix heat stabilizer is different than the copper based        heat stabilizer; and    -   the fibrous material is impregnated with the polyamide matrix        resin composition.

Preferably, in the composite structures of the invention, the matrixheat stabilizer is selected from dipentaerythritol, tripentaerythritol,pentaerythritol and mixtures of these. More preferably, the matrix heatstabilizer is selected from dipentaerythritol.

In a second aspect, the invention provides articles prepared from thecomposite structures of the invention.

In yet another aspect, the invention discloses and claims a process tomanufacture the composite structure of the invention.

DETAILED DESCRIPTION

The composite structures according to the present invention offer goodthermal stability during their manufacture, good heat aging properties,retention of mechanical properties after long-term high temperatureexposure. Furthermore, good retention of bond strength between thecomposite structure and the overmolding component is achieved in theovermolded composite structure.

For making overmolded composite structures and to increase theperformance of polymers, it is often desired to “overmold” one or morepolymer compositions onto the top portion, or all of the surfaces of acomponent so as to surround or encapsulate the component structure.Overmolding involves molding a second polymer (second component)directly onto one or more surfaces of the component structure (firstcomponent) to form an overmolded composite structure, wherein the firstcomponent and second component are adhered one to the other at least atone interface to make an overmolded composite structure. The firstcomponent can be a composite structure and the first component cancomprise various polymeric and fibrous materials. The polymercompositions of this invention used to impregnate fibrous materials ofthe first component or composite structure (i.e. the matrix polymercomposition) are different compositions from the resin(s) which comprisethe surface of the first component or composite structure (i.e. surfaceresin composition) but they may comprise the same polyamide polymer. Thefirst component or composite structure and the second component of theovermolded composite structure are desired to have good adhesion to eachother. The composite structure and/or overmolded composite structure aredesired to have good dimensional stability and retain their mechanicalproperties under adverse conditions, including thermal cycling.

Polyamides are excellent examples of polymers that can be used to makecomposite structures or overmolded composite structures due to theirexcellent mechanical properties. Unfortunately, polyamide compositionsmay suffer from an unacceptable deterioration of their mechanicalproperties during their manufacture and upon long-term high temperatureexposure during use and therefore, they may be non-ideal for makingovermolded composite structures used in highly demanding applicationssuch as the automotive field. Indeed, there is a current and generaldesire in the automotive field to have high temperature resistant,lightweight structures. Such high temperature resistant structures arerequired to maintain their mechanical properties when they are exposedto temperatures higher than 120° C. or even higher than 200° C., such asthose often reached in underhood areas of automobiles or to maintaintheir mechanical properties at an intermediate temperature, such as forexample 90° C., for long periods of time. When plastic parts are exposedto such combinations of time and temperature, it is a common phenomenonthat the mechanical properties tend to decrease due to thethermo-oxidation of the polymer. This phenomenon is called heat aging.

Unfortunately, the existing technologies fail to combine easy andefficient processability in terms of the impregnation rate of thefibrous material by a polymer with good thermal resistance, goodretention of mechanical properties against long-term high temperatureexposure, and excellent adhesion to overmolding compositions.

The present invention relates to composite structures and processes tomake them. The composite structure according to the present inventioncomprises at least one polyamide matrix resin impregnated into at leastone fibrous material and wherein the polyamide matrix resin comprises amatrix heat stabilizer. Preferably, the matrix heat stabilizer isselected from dipentaerythritol, tripentaerythritol, pentaerythritol andmixtures of these and even more preferably, the matrix heat stabilizeris dipentaerythritol. The composite structure additionally comprises apolyamide surface resin composition comprising a copper based heatstabilizer. The polyamide used in the polyamide matrix resin compositionand the polyamide surface resin composition can be the same polyamide ordifferent polyamides or blends of two or more polyamides.

The second component used to overmold the first component or compositestructure is a polyamide resin composition optionally comprising acopper based heat stabilizer and optionally comprising a reinforcingagent.

Definitions

As used throughout the specification, the phrases “about” and “at orabout” are intended to mean that the amount or value in question may bethe value designated or some other value about the same. The phrase isintended to convey that similar values promote equivalent results oreffects according to the invention.

As used herein, the term “overmolded composite structure” means astructure comprising a first component or a composite structure and asecond component. The second component is overmolded onto the firstcomponent or composite structure to make the overmolded compositestructure.

As used herein, the term “first component” or “composite structure”means a composition comprising at least one polyamide matrix resincomposition, at least one fibrous material, and a polyamide surfaceresin composition. The polyamide surface resin composition is theoutermost surface of the entire surface of the first component, orcomposite structure, or only a portion of the surface of the firstcomponent or composite structure depending on what percentage of thefirst component surface or composite structure surface is to beovermolded. The polyamide surface resin composition can be the outermosttop, the outermost bottom, or both the outermost top and outermostbottom surfaces of the first component or composite structure.

As used herein, the term “polyamide matrix resin” means the polyamideresin composition that is used to impregnate the fibrous material.

As used herein, the term “matrix heat stabilizer” means a stabilizerused in the polyamide matrix resin composition. The matrix heatstabilizer is not a copper based heat stabilizer and does not containcopper or copper ions.

As used herein, the term “fibrous material” means a material that is anysuitable mat, fabric, or web form known to those skilled in the art. Thefibers or strands used to form the fibrous material are interconnected(i.e. at least one fiber or strand is touching at least one other fiberor strand to form a continuous material) or touching each other so thata continuous mat, web or similar structure is formed.

As used herein, the term “polyamide surface resin” means a polyamidecomposition which comprises the outer surface of the first component orcomposite structure. The polyamide surface resin composition cancomprise the entire outer surface of the first component or compositestructure or a portion of the outer surface of the first component orcomposite structure depending on the end use.

As used herein, the term “copper based heat stabilizer” means a heatstabilizer that comprises a copper halide compound and a alkali metalhalide compound or combinations of different copper halides or alkalimetal halides.

As used herein, the term “second component” or “overmolding component”means a composition comprising a polyamide resin composition andoptionally a reinforcing agent. The second component is used to overmoldthe first component or composite structure.

As used herein, the term “overmolded” means molding and castingprocesses used to overmold a substrate, structure, or article with apolymeric composition. It is the process of molding over a substrate,structure, article, wherein the overmolding polymeric composition isbonded to and becomes an integral part of the substrate, structure, orarticle (i.e. the exterior part) upon cooling.

As used herein, the term “impregnated” means the polyamide matrix resincomposition flows into the cavities and void spaces of the fibrousmaterial As used herein, the term “bond strength” means the strength ofthe bond between the first component or composite structure and secondcomponent or overmolding component of the overmolded compositestructure.

As used herein, the term “heat aging” means exposing the componentstructure, the composite structure and/or the overmolded compositestructure to elevated temperatures for a given period of time.

As used herein, the term “high temperature long-term exposure” refers toa combination of exposure factors, i.e. time and temperature. Polymerswhich demonstrate heat aging performance under lab conditions or underconditions of the lifetime of the polymers such as those reached inunderhood areas of automobiles (e.g. at a temperature at or in excess of120° C., preferably at or in excess of 160° C., more preferably at or inexcess of 180° C. and still more preferably at or in excess of 200° C.and the aging or exposure being at or in excess of 500 hours andpreferably at or in excess of 1000 hours) can be shown to exhibitsimilar performance at lower temperatures for a much longer period ofaging or exposure. The temperature dependence of the rate constants ofpolymer degradation is known from the literature such as for example inJournal of Materials Science, 1999, 34, 843-849, and is described byArrhenius law; as an example aging at 180° C. for 500 hours ismore-or-less equivalent to aging at 80° C. for 12 years.

First Component or Composite Structure

The first component or composite structure comprises one or more fibrousmaterials impregnated with one or more polyamide matrix resincompositions and comprises one or more surface resin compositions. Thefirst component or composite structure can have a total thickness offrom about 50 to 20000 microns, preferably from about 50 to 5000microns, more preferably from about 500 to 3000 microns, and mostpreferably from about 800 to 2000 microns. The first component orcomposite structure can have multiple fibrous materials.

The polyamide surface resin composition may be both the top and bottomsurface of the first component or composite structure (essentiallycompletely encapsulating the first component or composite structure).Such a composition may be useful when it is desired to encapsulate orovermold the entire surface of the first component or compositestructure with the second component. The polyamide surface resincomposition may also be only the top or bottom surface, or a portion ofthe top or bottom surface of the first component or composite structuredepending on what percentage of the first component surface or compositestructure surface is to be overmolded.

If the first component or composite structure is to be overmolded onlyon one surface or part of surface, then the polyamide surface resincomposition may be present only on the surface or portion of the surfacethat is to be overmolded by the second component.

Fibrous Material

The fibrous material impregnated with the polyamide matrix resincomposition may be in any suitable mat, fabric, or web form known tothose skilled in the art. Suitable examples of such fibrous materialsinclude woven or nonwoven fabrics or mats, unidirectional strands offiber, and the like and different layers of fibrous material in thefirst component or composite structure may be formed from differentkinds of fibers, mats, or fabrics. The first component or compositestructure may contain multiple layers of fibrous materials which areimpregnated with one or more polyamide matrix resin compositions.Additionally, any given fibrous layer may be formed from two or morekinds of fibers (e.g., carbon and glass fibers). The fibers may beunidirectional, bi directional, or multidirectional. Preimpregnatedunidirectional fibers and fiber bundles may be formed into woven ornonwoven mats or other structures suitable for forming the fibrousmaterial. The fibrous material may be in the form of a unidirectionalpreimpregnated material or a multiaxial laminate of a preimpregnatedmaterial.

The fibrous material is preferably selected from woven or non-wovenstructures (e.g., mats, felts, fabrics and webs) textiles, fibrousbattings, a mixture of two or more materials, and combinations thereof.Non-woven structures can be selected from random fiber orientation oraligned fibrous structures. Examples of random fiber orientation includewithout limitation material which can be in the form of a mat, a needledmat or a felt. Examples of aligned fibrous structures include withoutlimitation unidirectional fiber strands, bidirectional strands,multidirectional strands, multi-axial textiles. Textiles can be selectedfrom woven forms, knits, braids and combinations thereof.

As used herein, the term “a fibrous material being impregnated with apolyamide matrix resin composition” means that the polyamide matrixresin composition encapsulates and embeds the fibrous material so as toform an interpenetrating network of fibrous material substantiallysurrounded by the matrix resin composition. For purposes herein, theterm “fiber” is defined as a macroscopically homogeneous body having ahigh ratio of length to width across its cross-sectional areaperpendicular to its length. The fiber cross section can be any shape,but is typically round or oval shaped. Depending on the end-useapplication of the composite structure and/or overmolded compositestructure and the required mechanical properties, more than one fibrousmaterial can be used, either by using several of the same fibrousmaterials or a combination of different fibrous materials. An example ofa combination of different fibrous materials is a combination comprisinga non-woven structure such as for example a planar random mat which isplaced as a central layer and one or more woven continuous fibrousmaterials that are placed as outside layers or layers above or below orboth above and below the central layer. Such a combination allows animprovement of the processing and thereof of the homogeneity of thefirst component or composite structure thus leading to improvedmechanical properties of the composite structure and/or overmoldedcomposite structure. The fibrous material may be made of any suitablematerial or a mixture of materials provided that the material or themixture of materials withstand the processing conditions used during theimpregnation by the polyamide matrix resin composition and the polyamidesurface resin composition and during overmolding of the first componentor composite structure by the second component.

Preferably, the fibrous material comprises glass fibers, carbon fibers,aramid fibers, graphite fibers, metal fibers, ceramic fibers, naturalfibers or mixtures thereof; more preferably, the fibrous materialcomprises glass fibers, carbon fibers, aramid fibers, natural fibers ormixtures thereof; and still more preferably, the fibrous materialcomprises glass fibers, carbon fibers and aramid fibers or mixturemixtures thereof. By natural fiber, it is meant any material of plantorigin or of animal origin. When used, the natural fibers are preferablyderived from vegetable sources such as for example from seed hair (e.g.cotton), stem plants (e.g. hemp, flax, bamboo; both bast and corefibers), leaf plants (e.g. sisal and abaca), agricultural fibers (e.g.,cereal straw, corn cobs, rice hulls and coconut hair) or lignocellulosicfiber (e.g. wood, wood fibers, wood flour, paper and wood-relatedmaterials). As mentioned above, more than one fibrous materials can beused. A combination of fibrous materials made of different fibers can beused such as for example a first component or composite structurecomprising one or more central layers made of glass fibers or naturalfibers and one or more outer layers (relative to central layer) made ofcarbon fibers or glass fibers. Preferably, the fibrous material isselected from woven structures, non-woven structures or combinationsthereof, wherein said structures are made of glass fibers and whereinthe glass fibers are E-glass filaments with a diameter between 8 and 30μm and preferably with a diameter between 10 to 24 μm. The fibrousmaterial used in the first component or composite structure of theinvention cannot be chopped fibers or particles. To be clear, thefibrous material in the first component or composite structure cannot befibers or particles which are not interconnected to form a continuousmat, web or similar layered structure. In other words, they cannot beindependent or single fibers or particles surrounded by the polyamidematrix resin composition.

The fibrous material may further comprise a thermoplastic material, forexample the fibrous material may be in the form of commingled orco-woven yarns or a fibrous material impregnated with a powder made of athermoplastic material that is suited to subsequent processing intowoven or non-woven forms, or a mixture for use as a uni-directionalmaterial.

Preferably, the ratio between the fibrous material and the polymermaterials in the first component or composite structure (i.e. thefibrous material in combination with the matrix resin composition andthe surface resin composition), is at least 30 percent fibrous materialand more preferably between 40 and 60 percent fibrous material, thepercentage being a volume-percentage based on the total volume of thefirst component structure or composite structure.

Copper Based Heat Stabilizer

The heat stabilizer used in the polyamide surface resin composition(first component or composite structure) and optionally in the secondcomponent is a copper halide based inorganic heat stabilizer. The heatstabilizer comprises at least one copper halide or copper acetate and atleast one alkali metal halide. Nonlimiting examples of copper halideinclude copper iodide and copper bromide. The alkali metal halide isselected from the group consisting of the iodides and bromides oflithium, sodium, and potassium with potassium iodide or bromide beingpreferred. Preferably, the copper based heat stabilizer is a mixture of10 to 50 weight percent copper halide, 50 to 90 weight percent potassiumiodide, and from zero to 15 weight percent metal stearate. Even morepreferably, the copper based heat stabilizer is a mixture of 10 to 30weight percent copper halide, 70 to 90 weight percent potassium iodide,and from zero to 15 weight percent metal stearate and most preferablythe copper based heat stabilizer is a mixture of 10 to 20 weight percentcopper halide, 75 to 90 weight percent potassium iodide, and from zeroto 12 weight percent metal stearate. An example of a copper based heatstabilizer of the invention is Polyadd P201 from Ciba SpecialtyChemicals comprising a blend of 7:1:1 weight ratio (approximately78:11:11 percent ratio by weight) of potassium iodide, cuprous iodide,and aluminum stearate respectively. A preferred heat stabilizer is amixture of copper iodide and potassium iodide (Cul/KI). The heatstabilizer is present in an amount from at or about 0.1 to at or about 3weight percent, preferably from at or about 0.1 to at or about 1.5weight percent, or more preferably from at or about 0.1 to at or about1.0 weight percent, the weight percentage being based on the totalweight of the polyamide surface resin composition in the first componentor composite structure or based on the total weight of the polyamideresin composition of the second component, as the case may be. Theamount of copper halide based heat stabilizer in the polyamide surfaceresin composition or the polyamide resin composition of the secondcomponent will depend on the anticipated use. If extremely hightemperature environments are envisioned, then a higher concentration ofcopper halide heat stabilizer is needed.

Matrix Heat Stabilizer

The matrix heat stabilizer of the polyamide matrix resin composition isdifferent than the copper based heat stabilizer of the polyamide surfaceresin composition. The one or more matrix heat stabilizers in thepolyamide matrix resin composition are present in an amount from 0 to ator about 3 weight percent, preferably from at or about 0.1 to at orabout 3 weight percent, more preferably from at or about 0.1 to at orabout 1 weight percent, or more preferably from at or about 0.1 to at orabout 0.7 weight percent, the weight percentage being based on the totalweight of the polyamide matrix resin composition in the first componentor composite structure.

The matrix heat stabilizer used in the polyamide matrix resincomposition can be any heat stabilizer as long as it is not a copperhalide based heat stabilizer. Heat stabilizers useful in the polyamidematrix resin composition include polyhydric alcohols having more thantwo hydroxyl groups. The one or more polyhydric alcohols may beindependently selected from aliphatic hydroxylic compounds containingmore than two hydroxyl groups, aliphatic-cycloaliphatic compoundscontaining more than two hydroxyl groups, cycloaliphatic compoundscontaining more than two hydroxyl groups and saccharides containing morethan two hydroxyl groups.

An aliphatic chain in the polyhydric alcohol can include not only carbonatoms but also one or more hetero atoms which may be selected, forexample, from nitrogen, oxygen and sulphur atoms. A cycloaliphatic ringpresent in the polyhydric alcohol can be monocyclic or part of abicyclic or polycyclic ring system and may be carbocyclic orheterocyclic. A heterocyclic ring present in the polyhydric alcohol canbe monocyclic or part of a bicyclic or polycyclic ring system and mayinclude one or more hetero atoms which may be selected, for example,from nitrogen, oxygen and sulphur atoms. The one or more polyhydricalcohols may contain one or more substituents, such as ether, carboxylicacid, carboxylic acid amide or carboxylic acid ester groups.

Examples of polyhydric alcohols containing more than two hydroxyl groupsinclude, without limitation, triols, such as glycerol,trimethylolpropane, 2,3-di-(2′-hydroxyethyl)cyclohexan-1-ol,hexane-1,2,6-triol, 1,1,1-tris-(hydroxymethyl)ethane,3-(2′-hydroxyethoxy)-propane-1,2-diol,3-(2′-hydroxypropoxy)-propane-1,2-diol,2-(2′-hydroxyethoxy)-hexane-1,2-diol,6-(2′-hydroxypropoxy)-hexane-1,2-diol,1,1,1-tris-[(2′-hydroxyethoxy)-methyl]-ethane,1,1,1-tris-[(2′-hydroxypropoxy)-methyl]-propane,1,1,1-tris-(4′-hydroxyphenyl)-ethane,1,1,1-tris-(hydroxyphenyl)-propane,1,1,3-tris-(dihydroxy-3-methylphenyl)-propane,1,1,4-tris-(dihydroxyphenyl)-butane,1,1,5-tris-(hydroxyphenyl)-3-methylpentane, di-trimethylopropane,trimethylolpropane ethoxylates, or trimethylolpropane propoxylates;polyols such as pentaerythritol, dipentaerythritol, andtripentaerythritol; and saccharides containing more than two hydroxylgroups, such as cyclodextrin, D-mannose, glucose, galactose, sucrose,fructose, xylose, arabinose, D-mannitol, D-sorbitol, D-or L-arabitol,xylitol, iditol, talitol, allitol, altritol, guilitol, erythritol,threitol, and D-gulonic-y-lactone and the like.

Preferred polyhydric alcohols include those having a pair of hydroxylgroups which are attached to respective carbon atoms which are separatedone from another by at least one atom. Especially preferred polyhydricalcohols are those in which a pair of hydroxyl groups is attached torespective carbon atoms which are separated one from another by a singlecarbon atom. Preferably, the one or more polyhydric alcohols comprisedin the polyamide matrix resin composition described herein areindependently selected from pentaerythritol, dipentaerythritol,tripentaerythritol, di-trimethylopropane, D-mannitol, D-sorbitol,xylitol and mixtures thereof. More preferably, the one or morepolyhydric alcohols comprised in the polyamide composition describedherein are independently selected from dipentaerythritol,tripentaerythritol, pentaerythritol and mixtures thereof. Still morepreferably, the one or more polyhydric alcohols comprised in thepolyamide composition described herein are dipentaerythritol and/orpentaerythritol.

The one or more polyhydric alcohols are present in the polyamide matrixresin composition described herein from 0.25 weight percent to 15 weightpercent, more preferably from 0.5 weight percent to 10 weight percentand still more preferably from 0.5 weight percent to 5 weight percent,the weight percentages being based on the total weight of the polyamidematrix resin composition in the first component or composite structure.

Preferably, the one or more polyhydric alcohols comprised in thepolyamide composition described herein are dipentaerythritol and/orpentaerythritol and are present in the polyamide matrix resincomposition described herein from at or about 0.1 to at or about 3weight percent, more preferably from at or about 0.1 to at or about 1weight percent, or more preferably from at or about 0.1 to at or about0.7 weight percent, the weight percentage being based on the totalweight of the polyamide matrix resin composition in the first componentor composite structure.

Polyamide Resins

Polyamide resins used in the manufacture of the composite structure ofthe invention and/or in the manufacture of the overmolded compositestructure are condensation products of one or more dicarboxylic acidsand one or more diamines, and/or one or more aminocarboxylic acids,and/or ring-opening polymerization products of one or more cycliclactams. The polyamide resins are selected from fully aliphaticpolyamide resins, semi-aromatic polyamide resins and mixtures thereof.The term “semi-aromatic” describes polyamide resins that comprise atleast some aromatic carboxylic acid monomer(s) and aliphatic diaminemonomer(s), in comparison with “fully aliphatic” which describespolyamide resins comprising aliphatic carboxylic acid monomer(s) andaliphatic diamine monomer(s).

Fully aliphatic polyamide resins are formed from aliphatic and alicyclicmonomers such as diamines, dicarboxylic acids, lactams, aminocarboxylicacids, and their reactive equivalents. A suitable aminocarboxylic acidincludes 11-aminododecanoic acid. In the context of this invention, theterm “fully aliphatic polyamide resin” refers to copolymers derived fromtwo or more such monomers and blends of two or more fully aliphaticpolyamide resins. Linear, branched, and cyclic monomers may be used.

Carboxylic acid monomers useful in the preparation of fully aliphaticpolyamide resins include, but are not limited to, aliphatic carboxylicacids, such as for example adipic acid (C6), pimelic acid (C7), subericacid (C8), azelaic acid (C9), sebacic acid (C10), dodecanedioic acid(C12) and tetradecanedioic acid (C14). Useful diamines include thosehaving four or more carbon atoms, including, but not limited totetramethylene diamine, hexamethylene diamine, octamethylene diamine,decamethylene diamine, 2-methylpentamethylene diamine,2-ethyltetramethylene diamine, 2-methyloctamethylene diamine;trimethylhexamethylene diamine and/or mixtures thereof. Suitableexamples of fully aliphatic polyamide resins include PA6; PA6,6; PA4,6;PA6,10; PA6,12; PA6,14; P 6,13; PA 6,15; PA6,16; PA11; PA 12; PA10; PA9,12; PA9,13; PA9,14; PA9,15; PA6,16; PA9,36; PA10,10; PA10,12; PA10,13;PA10,14; PA12,10; PA12,12; PA12,13; PA12,14 and copolymers and blends ofthe same. Preferred examples of fully aliphatic polyamide resinscomprised in the polyamide compositions described herein include PA6;PA11; PA12; PA4,6; PA6,6; PA,10; PA6,12; PA10,10 and copolymers andblends of the same.

Semi-aromatic polyamide resins are homopolymers, copolymers,terpolymers, or higher polymers wherein at least a portion of the acidmonomers are selected from one or more aromatic carboxylic acids. Theone or more aromatic carboxylic acids can be terephthalic acid ormixtures of terephthalic acid and one or more other carboxylic acids,like isophthalic acid, substituted phthalic acid such as for example2-methylterephthalic acid and unsubstituted or substituted isomers ofnaphthalenedicarboxylic acid, wherein the carboxylic acid componentpreferably contains at least 55 mole percent of terephthalic acid (themole percent being based on the carboxylic acid mixture). Preferably,the one or more aromatic carboxylic acids are selected from terephthalicacid, isophthalic acid and mixtures thereof and more preferably, the oneor more carboxylic acids are mixtures of terephthalic acid andisophthalic acid, wherein the mixture preferably contains at least 55mole percent of terephthalic acid. Furthermore, the one or morecarboxylic acids can be mixed with one or more aliphatic carboxylicacids, like adipic acid; pimelic acid; suberic acid; azelaic acid;sebacic acid and dodecanedioic acid, adipic acid being preferred. Morepreferably the mixture of terephthalic acid and adipic acid comprised inthe one or more carboxylic acids mixtures of the semi-aromatic polyamideresin contains at least 25 mole percent of terephthalic acid.Semi-aromatic polyamide resins comprise one or more diamines that can bechosen among diamines having four or more carbon atoms, including, butnot limited to tetramethylene diamine, hexamethylene diamine,octamethylene diamine, nonamethylene diamine, decamethylene diamine,2-methylpentamethylene diamine, 2-ethyltetramethylene diamine,2-methyloctamethylene diamine; trimethylhexamethylene diamine,bis(p-aminocyclohexyl)methane; m-xylylene diamine; p-xylylene diamineand/or mixtures thereof. Suitable examples of semi-aromatic polyamideresins include poly(hexamethylene terephthalamide) (polyamide 6,T),poly(nonamethylene terephthalamide) (polyamide 9,T), poly(decamethyleneterephthalamide) (polyamide 10,T), poly(dodecamethylene terephthalamide)(polyamide 12,T), hexamethylene adipamide/hexamethylene terephthalamidecopolyamide (polyamide 6,T/6,6), hexamethyleneterephthalamide/hexamethylene isophthalamide (6,T/6,I), poly(m-xylyleneadipamide) (polyamide MXD,6), hexamethylene adipamide/hexamethyleneterephthalamide copolyamide (polyamide 6,T/6,6), hexamethyleneterephthalamide/2-methylpentamethylene terephthalamide copolyamide(polyamide 6,T/D,T), hexamethylene adipamide/hexamethyleneterephthalamide/hexamethylene isophthalamide copolyamide (polyamide6,6/6,T/6,I); poly(caprolactam-hexamethylene terephthalamide) (polyamide6/6,T) and copolymers and blends of the same. Preferred examples ofsemi-aromatic polyamide resins comprised in the polyamide compositiondescribed herein include PA6,T; PA6,T/6,6, PA6,T/6,I; PAMXD,6; PA6,T/D,Tand copolymers and blends of the same.

Any combination of aliphatic or semi-aromatic polyamides can be used asthe polyamide for the polyamide matrix resin composition, polyamidesurface resin composition, and the polyamide resin of the secondcomponent. It is within the normal skill of one in the art to selectappropriate combinations of polyamides depending on the end use.

Second Component or Overmolding Component

The second component of the overmolded composite structure used toovermold the first component or composite structure is a polyamide resincomposition optionally comprising a copper based heat stabilizer asdescribed above and optionally a reinforcing agent. The one or morepolyamides may be the same or different from the one or more polyamidesof the first component or composite structure matrix resin and surfaceresin composition.

Reinforcing Agent

The polyamide resin composition of the second component may furthercomprise one or more reinforcing agents such as glass fibers, glassflakes, carbon fibers, mica, wollastonite, calcium carbonate, talc,calcined clay, kaolin, magnesium sulfate, magnesium silicate, bariumsulfate, titanium dioxide, sodium aluminum carbonate, barium ferrite,and potassium titanate. The reinforcing agent in the second componentcannot be a mat or woven fabric such as those used in the firstcomponent or composite structure. Preferably, the reinforcing agentcomprises independent fibers or particles uniformly blended into thepolyamide. Any reinforcing agent used in the second component must allowthe polyamide resin composition to be injection or flow molded. Whenpresent, the one or more reinforcing agents are present in an amountfrom at or about 1 to at or about 60 weight percent, preferably from ator about 1 to at or about 40 weight percent, or more preferably from ator about 1 to at or about 35 weight percent, the weight percentagesbeing based on the total weight of the polyamide resin composition ofthe second component.

Overmolded Composite Structure

Addition of matrix and copper based heat stabilizers to the componentsof the invention improves thermal stability of the first component orcomposite structure and optionally of the second component duringprocessing as well as upon use and time of the composite structure orovermolded composite structure. In addition to the improved heatstability, the presence of heat stabilizers may allow an increase of thetemperature that is used during the impregnation of the fibrousmaterial, thus reducing the melt viscosity of the matrix resin describedherein. As a consequence of a reduced melt viscosity of the matrixresin, impregnation rates of the fibrous material may be increased.

The use of different heat stabilizers in the polyamide matrix resincomposition and the polyamide surface resin composition of the firstcomponent or composite structure is an important aspect of theinvention. The use of a copper based heat stabilizer in the polyamidesurface resin composition and optionally in the second componentimproves bond strength of the second component to the first component orcomposite structure while simultaneously providing adequate heat agingproperties of the overmolded composite structure.

In a preferred embodiment, the matrix heat stabilizer is selected fromdipentaerythritol, tripentaerythritol, pentaerythritol and mixtures ofthese and the surface heat stabilizer in the surface resin compositionis a copper based heat stabilizer.

The overmolded composite structure comprises a second componentovermolded onto the first component or composite structure. The secondcomponent is adhered to the first component or composite structuredescribed above over at least a portion of the top or bottom surface ofthe first component or composite structure, the entire top or bottomsurface of the first component or composite structure, or both, orcompletely encapsulates the first component or composite structure.Regardless of what portion of the surface of the first component orcomposite structure is overmolded, the surface of the first component orcomposite structure that is overmolded must comprise the polyamidesurface resin composition to assure good bond strength of the first andsecond components. The second component comprises one or more polyamideresin compositions selected from aliphatic polyamide resins,semi-aromatic polyamide resins, or combinations thereof such as thosedescribed above.

Additives

The polyamide resin of any component of the composite structure orovermolded composite structure may further comprise one or more commonadditives, including, without limitation, ultraviolet light stabilizers,flame retardant agents, flow enhancing additives, lubricants, antistaticagents, coloring agents (including dyes, pigments, carbon black, and thelike), nucleating agents, crystallization promoting agents and otherprocessing aids or mixtures thereof known in the polymer compoundingart.

Fillers, modifiers and other ingredients described above may be presentin amounts and in forms well known in the art, including in the form ofso-called nano-materials where at least one of the dimensions of theparticles is in the range of 1 to 1000 nm.

Preferably, any additives, including heat stabilizers but excludingfibrous materials used in the first component or composite structure ofthe invention, added to the polyamide resins used in any component ofthe composite structure and/or overmolded composite structure arewell-dispersed within the polyamide resin. Any melt-mixing method may beused to combine the polyamide resins and additives of the presentinvention. For example, the polyamide resins and additives may be addedto a melt mixer, such as, for example, a single or twin-screw extruder;a blender; a single or twin-screw kneader; or a Banbury mixer, eitherall at once through a single step addition, or in a stepwise fashion,and then melt-mixed. When adding the polyamide resins and additionaladditives in a stepwise fashion, part of the polyamide resin and/oradditives are first added and melt-mixed with the remaining polyamideresin(s) and additives being subsequently added and further melt-mixeduntil a well-mixed or homogeneous composition is obtained.

The overmolded composite structure according to the present inventionmay be manufactured by a process comprising a step of overmolding thefirst component or composite structure with the second component. By“overmolding”, it is meant that the second component is molded orextruded onto at least one portion of the surface of the first componentor composite structure.

In one example of an overmolding process, the second component isinjected into a mold already containing the first component or compositestructure, the latter having been manufactured beforehand as describedhereafter, so that the first and second components are adhered to eachother over at least a portion of the surface of the first component orcomposite structure. The first component or composite structure ispositioned in a mold having a cavity defining the outer surface of thefinal overmolded composite structure. The second component may beovermolded on one side or on both sides of the first component orcomposite structure and it may fully or partially encapsulate the firstcomponent or composite structure. After having positioned the firstcomponent or composite structure in the mold, the second component isthen introduced in molten form. The two components are preferablyadhered together by injection or compression molding as an overmoldingstep, and more preferably by injection molding.

The first component or composite structure can be made by a process thatcomprises a step of impregnating the fibrous material with the polyamidematrix resin composition, wherein at least a portion of the surface ofthe first component or composite structure comprises the polyamidesurface resin composition. Preferably, the fibrous material isimpregnated with the polyamide matrix resin composition bythermopressing. During thermopressing, the fibrous material(s), thepolyamide matrix resin composition and the polyamide surface resincomposition undergo heat and pressure in order to allow the polymers tomelt and penetrate through the fibrous material and, therefore, toimpregnate said fibrous material.

Typically, thermopressing is made at a pressure between 2 and 100 barsand more preferably between 10 and 40 bars and a temperature which isabove the melting point of the polyamide matrix resin composition andthe polyamide surface resin composition, preferably at least about 20°C. above the melting point to enable a proper impregnation. Heating maybe done by a variety of means, including contact heating, radiant gasheating, infra red heating, convection or forced convection, inductionheating, microwave heating or combinations thereof. Even though thepolyamide compositions are in the melt state during thermopressing, thepolyamide surface resin composition does not migrate from the surface toany significant degree. After thermopressing, the first component orcomposite structure is no longer considered a laminate structure havingseparate layers but a unified component structure.

Due to the improved heat stability obtained by adding a matrix heatstabilizer to the polyamide matrix resin composition, the temperaturethat is used during the impregnation of the fibrous material can beincreased relative to a polyamide resin composition without a matrixheat stabilizer. The reduced melt viscosity of the polyamide matrixresin composition obtained by this increase of temperature allows a morerapid impregnation rate of the fibrous material which translates into afaster overall manufacturing cycle for the composite structure and/orovermolded composite structure. Addition of the copper halide based heatstabilizer to the polyamide surface resin composition provides heatstability to the polyamide surface resin composition during theimpregnation and additionally provides improved bond strength of thesecond component to the first component or composite structure of theovermolded composite structure.

Pressure used during the impregnation process can be applied by a staticprocess or by a continuous process (also known as a dynamic process), acontinuous process being preferred for reasons of speed. Examples ofimpregnation processes include without limitation vacuum molding,in-mold coating, cross-die extrusion, pultrusion, wire coating typeprocesses, lamination, stamping, diaphragm forming or press-molding,lamination being preferred.

One example of a process used to impregnate the fibrous material is alamination process. The first step of the lamination process involvesheat and pressure being applied to the fibrous material, the polyamidematrix resin composition and the polyamide surface resin compositionthrough opposing pressured rollers or belts in a heating zone,preferably followed by the continued application of pressure in acooling zone to finalize consolidation and cool the impregnated fibrousmaterial by pressurized means. Examples of lamination techniques includewithout limitation calendering, flatbed lamination and double-belt presslamination. When lamination is used as the impregnating process,preferably a double-belt press is used for lamination. The laminationprocess may comprise various layer combinations of the polyamide matrixresin composition and the fibrous material. The polyamide surface resincomposition is always used as the top layer or both the top and bottomlayer during the lamination process. For example, the multi-layerlaminate may comprise two polyamide matrix resin composition layers, onelayer of woven continuous glass fiber textile as the fibrous layer, twopolyamide matrix resin composition layers, one layer of woven continuousglass fiber textile, two polyamide matrix resin composition layers, onelayer of woven continuous glass fiber textile and two polyamide surfacelayers to make an 11 layer laminate. After impregnation of the fibrousmaterials using the lamination process, the end product is the firstcomponent or composite structure of the invention which can then beovermolded. A first component or composite structure prepared by thisprocess is no longer a multi-layer laminate but a unified structure (apolymer continuum) with no discernable individual layers.

The polyamide matrix resin composition and the polyamide surface resincomposition can also be applied to the fibrous material by conventionalmeans such as for example powder coating, film lamination, extrusioncoating or a combination of two or more thereof, provided that thepolyamide surface resin composition is applied on at least a portion ofthe surface of the first component or composite structure so as to beaccessible when the polyamide overmolding resin composition is appliedonto at least a portion of the surface of the first component orcomposite structure.

During a powder coating process, a polymer powder which has beenobtained by conventional grinding methods is applied to the fibrousmaterial. The powder may be applied onto the fibrous material byscattering, sprinkling, spraying, thermal or flame spraying, orfluidized bed coating methods. Multiple powder coating layers can beapplied to the fibrous material. Optionally, the powder coating processmay further comprise a step which consists in a post sintering step ofthe powder on the fibrous material. The polyamide matrix resincomposition and the polyamide surface resin composition are applied tothe fibrous material such that at least a portion of the surface of thefirst component or composite structure comprises the polyamide surfaceresin composition. Subsequently, thermopressing is performed on thepowder coated fibrous material, with an optional preheating of thepowder coated fibrous material outside of the pressurized zone.

During film lamination, one or more films comprising the polyamidematrix resin composition and one or more films made of the polyamidesurface resin composition which have been obtained by conventionalextrusion methods known in the art such as for example blow filmextrusion, cast film extrusion and cast sheet extrusion are applied toone or more layers of the fibrous material, e.g. by layering. Thepolyamide surface resin composition is again the top or bottom or bothtop and bottom layers of the film laminate before thermopressing.Subsequently, thermopressing is performed on the film laminatecomprising the one or more films made of the polyamide matrix resincomposition, the polyamide surface resin composition, and the one ormore fibrous materials. During thermopressing, the films melt andpenetrate around the fibrous material as a polymer continuum surroundingthe fibrous material with the polyamide matrix resin. The polyamidesurface resin composition remains on the surface of the first componentor composite structure.

During extrusion coating, pellets and/or granulates made of the matrixresin composition and pellets and/or granulates made of the surfaceresin composition are melted and extruded through one or more flat diesso as to form one or more melt curtains which are then applied onto thefibrous material by laying down the one or more melt curtains in amanner similar to the film lamination procedure. Subsequently,thermopressing is performed on the layered structure to provide thefirst component or composite structure of the invention.

With the aim of improving bond strength between the first component orcomposite structure and the second component, the first component orcomposite structure is typically heated at a temperature close to butbelow the melt temperature of the polyamide matrix resin compositionprior to the overmolding step and then the heated first component orcomposite structure is rapidly transferred into the heated mold thatwill be used for the overmolding step. Such a preheating step may bedone by a variety of means, including contact heating, radiant gasheating, infra red heating, convection or forced convection air heating,induction heating, microwave heating or combinations thereof.

Depending on the end-use application, the first component or compositestructure may be shaped into a desired geometry or configuration, orused in sheet form prior to the overmolding step. The first component orcomposite structure may be flexible, in which case it can be rolled andthen unrolled for overmolding.

One process for shaping the first component or composite structurecomprises a step of shaping the first component or composite structureafter the impregnating step. Shaping the first component or compositestructure may be done by compression molding, stamping or any techniqueusing heat and/or pressure, compression molding and stamping beingpreferred. Preferably, pressure is applied by using a hydraulic moldingpress. During compression molding or stamping, the composite structureis preheated to a temperature above the melt temperature of thepolyamide surface resin composition and preferably above the melttemperature of the polyamide matrix resin composition by heated meansand is transferred to a forming or shaping means such as a molding presscontaining a mold having a cavity of the shape of the final desiredgeometry whereby it is shaped into a desired configuration and isthereafter removed from the press or the mold after cooling to atemperature below the melt temperature of the polyamide surface resincomposition and preferably below the melt temperature of the polyamidematrix resin composition.

One problem during the manufacture of composite structures and/orovermolded composite structures is related to the thermo-oxidation anddegradation of the first component or composite structure and especiallythe thermal degradation of the surface of the first component orcomposite structure during the preheating step(s) described above andduring the shaping step. The present invention not only provides a firstcomponent or composite structure having good heat stability but alsoprovides a first component or composite structure having excellent bondstrength to the second component. This leads to composite structuresand/or overmolded composite structures that resist degradation ofmechanical performance during exposure to high temperature operationalmanufacturing environments and provides excellent long term flexuralstrength (bond strength).

With the aim of improving adhesion between the first component orcomposite structure and second component of the overmolded compositestructure, the surface of the first component or composite structure maybe a textured surface so as to increase the relative surface availablefor overmolding. Such textured surfaces may be obtained during theshaping step by using a press or a mold having for example porosities orindentations on its surface.

Alternatively, a one step process comprising the steps of shaping andovermolding the first component or composite structure in a singlemolding station may be used. This one step process avoids the step ofcompression molding or stamping the first component or compositestructure in a mold or press and avoids the optional preheating step andthe transfer of the preheated first component or composite structure tothe molding station or cavity. During this one step process, the firstcomponent or composite structure is heated outside, adjacent to orwithin the molding station at a temperature at which the first componentor composite structure is conformable or shapable during the overmoldingstep, preferably the first component or composite structure is heated toa temperature above its melt temperature. The shape of the firstcomponent or composite structure is conferred by the mold followed byovermolding.

The composite structures and/or overmolded composite structuresaccording to the present invention may be used in a wide variety ofapplications such as for example components for automobiles, trucks,commercial airplanes, aerospace, rail, household appliances, computerhardware, portable hand held electronic devices, recreation and sportsequipment, structural component for machines, buildings, photovoltaicequipment or mechanical devices.

Examples of automotive applications include, without limitation, seatingcomponents and seating frames, engine cover brackets, engine cradles,suspension arms and cradles, spare tire wells, chassis reinforcement,floor pans, front-end modules, steering column frames, instrumentpanels, door systems, body panels (such as horizontal body panels anddoor panels), tailgates, hardtop frame structures, convertible top framestructures, roofing structures, engine covers, housings for transmissionand power delivery components, oil pans, airbag housing canisters,automotive interior impact structures, engine support brackets, crosscar beams, bumper beams, pedestrian safety beams, firewalls, rear parcelshelves, cross vehicle bulkheads, pressure vessels such as refrigerantbottles, fire extinguishers, and truck compressed air brake systemvessels, hybrid internal combustion/electric or electric vehicle batterytrays, automotive suspension wishbone and control arms, suspensionstabilizer links, leaf springs, vehicle wheels, recreational vehicle andmotorcycle swing arms, fenders, roofing frames and tank flaps.

Examples of household appliances include without limitation washers,dryers, refrigerators, air conditioning and heating. Examples ofrecreation and sports include without limitation inline-skatecomponents, baseball bats, hockey sticks, ski and snowboard bindings,rucksack backs and frames, and bicycle frames. Examples of structuralcomponents for machines include electrical/electronic parts such as forexample housings for hand held electronic devices, and computers.

Preferably, the composite structures and/or overmolded compositestructures of the invention are used as under the hood automotivecomponents where high temperature environments exist.

EXAMPLES

The following materials were used for preparing examples (abbreviated as“E” in the table) of composites structures according to the presentinvention and comparative examples (abbreviated as “C” in the table) ofcomposite structures.

-   Polyamide 1 (PA1): polyamide comprising adipic acid and    1,6-hexamethylenediamine with a weight average molecular weight of    around 32000 Daltons and is commercially available from E. I. du    Pont de Nemours and Company as PA66. PA1 has a melting point of    about 260° C. to about 265° C. and a glass transition of about    40° C. to about 70° C., measured by DSC Instrument first heating    scan at 10° C./min.-   Polyhydric alcohol based heat stabilizer (DPE): dipentaerythritol    commercially available from Perstorp Speciality Chemicals AB,    Perstorp, Sweden as Di-Penta 93.-   Copper based heat stabilizer (Cul/KI): a blend of 7-1-1 (by weight)    blend of potassium iodide, cuprous iodide, and aluminum stearate,    available from Ciba Specialty Chemicals.

Preparation of Films

Matrix resin compositions and surface resin compositions of example E1and comparative examples C1, C2, C3 and C4 shown in Table 1 were meltedor melt-blended in a twin-screw extruder at about 280° C. The melted ormelt-blended polyamide compositions (Table 1) were made into films byexiting the extruder through an adaptor and a film die at about 280° C.and cast onto a casting drum oil-heated at 100° C., then drawn in airand wound around a core at room temperature. The matrix resin andsurface resin compositions were made into about a 250 micron thick film.The thickness of the films was controlled by the rate of drawing.

Preparation of the Composite Structures

Preparation of the composite structures of example E1 and comparativeexamples C1 to C4 was accomplished by first making a seven layerlaminate having a thickness of about 1.5 mm. The laminate comprisesmultiple layers of film of compositions shown in table 1 and wovencontinuous glass fiber textile (prepared from E-glass fibers having adiameter of 17 microns, sized with 0.4% of a silane-based sizing agentand a nominal roving tex of 1200 g/km that have been woven into a 2/2twill (balanced weave) with an areal weight of 600 g/m²) in thefollowing sequence: two layers of film of surface resin composition, onelayer of woven continuous glass fiber textile, two layers of film ofmatrix resin composition, one layer of woven continuous glass fibertextile, two layers of film of matrix resin composition, one layer ofwoven continuous glass fiber textile and two layers of film of surfaceresin composition. The laminates were compression molded by a Dake Press(Grand Haven, Mich.) Model 44-225 (pressure range 0-25K) with an 8 inchplatten. A 6×6″ specimen of film and glass textile layers as describedabove was placed in the mold and heated to a temperature of about 320°C., held at the temperature for 2 minutes without pressure, then pressedat the 320° C. temperature with the following pressures: about 6 bar forabout 2 minutes, then with about 22 bar for about 2 additional minutes,and then with about 45 bar for about 2 additional minutes; it wassubsequently cooled to ambient temperature. The thusly formed compositestructure had a thickness of about 1.6 mm. The composite structures hadmelting ranges between about 245° C. (onset of melting) to about 268° C.(completion of melting) with melting peaks at about 260° C. to about265° C., measured by DSC Instrument first heating scan at 10° C./min.

Heat Ageing

The composite structures obtained as described above were cut into ½″(about 12.7 mm) by 3″ (about 76 mm) long tests specimens (bars) using aMK-377 Tile Saw with a diamond edged blade and water as a lubricant.Half of the specimens were then heat aged in a re-circulating air ovenat 210° C. for 250 hours or for 500 hours.

Flex Strength of Composite Structures of Table 1

Flexural Strength was tested on the heat aged test specimens via a3-point bend test. The apparatus and geometry were according to ISOmethod 178, bending the specimen with a 2.0″ support width with theloading edge at the center of the span. The tests were conducted with 1KN load at 2 mm/min until fracture. The results are shown in Table 1,along with test results from the specimens that were not heat aged. The% retention of flex strength after heat aging is also recorded inTable 1. It is seen in Table 1 that example E1 containing the copperbased heat stabilizer in the surface resin composition and DPE in thematrix resin composition retains flexural strength after being heat agedin air at 210° C. for 250 hours (121% flexural strenght retention) andretains 46% flexural strength after being heat aged in air at 210° C.for 500 hours. In contrast, comparative examples C1, C2 , C3 and C4containing respectively, no heat stabilizers (C1), copper based heatstabilizer in both the matrix and surface resin composition (C2), DPE inboth the matrix and surface resin composition (C3), and both copperbased heat stabilizer and DPE in both the matrix and the surface resincomposition (C4) lose bond strength after heat aging in air at 210° C.for 250 hours and for 500 hours.

TABLE 1 E1 C1 C2 C3 C4 Matrix Resin Composition PA1 98.5 100.0 99.0 98.598.75 DPE 1.5 1.5 0.75 CuI/KI 1.0 0.5 Surface Resin Composition PA1 99.0100.0 99.0 98.5 98.75 DPE 1.5 0.75 CuI/KI 1.0 1.0 0.5 Flex Strength oflaminate ISO-178 (Mpa) As laminated 517 360 531 504 402 After 250 hrs inair 625 230 538 485 363 oven at 210° C. % Retention 121 64 101 96 90After 500 hrs in air 238 63 217 161 119 oven at 210° C. % Retention 4618 41 32 30

1. A composite structure comprising: a polyamide matrix resincomposition comprising from 0.1 to at or about 3 weight percent of amatrix heat stabilizer based on the weight of the polyamide matrix resincomposition; a fibrous material selected from woven or non-wovenstructures, felts, knits, braids, textiles, fibrous battings or mats,and combinations of these; and a polyamide surface resin compositioncomprising 0.1 to 3 weight percent of a copper based heat stabilizerbased on the weight of the polyamide surface resin composition wherein:the matrix heat stabilizer is different than the copper based heatstabilizer; and wherein the fibrous material is impregnated with thepolyamide matrix resin composition.
 2. The composite structure of claim1 wherein the polyamide in the matrix resin composition and thepolyamide in the surface resin composition, are independently selectedfrom the group consisting of PA6; PA11; PA12; PA4,6; PA6,6; PA,10;PA6,12; PA10,10; PA6T; PA6I, PA6I/6T; PA6,T/6,6; PAMXD6; PA6T/DT andcopolymers and blends of the same.
 3. The composite structure of claim 1wherein the matrix heat stabilizer is selected from the group consistingof dipentaerythritol, tripentaerythritol, pentaerythritol and mixturesthereof.
 4. The composite structure of claim 1 wherein the copper basedheat stabilizer is a mixture of 10 to 50 weight percent copper halide,50 to 90 weight percent potassium iodide, and from zero to 15 weightpercent metal stearate.
 5. The composite structure of claim 1 whereinthe fibrous material is from 30 weight percent to 60 volume percent ofthe composite structure.
 6. The composite structure of claim 1 whereinthe surface resin composition and/or the matrix resin compositionfurther comprise one or more impact modifiers, one or more oxidativestabilizers, one or more reinforcing agents, one or more ultravioletlight stabilizers, one or more flame retardant agents or mixturesthereof.
 7. An article made from the composite structure of claim
 1. 8.The article of claim 7 in the form of components for automobiles,trucks, commercial airplanes, aerospace, rail, household appliances,computer hardware, hand held devices, recreation and sports, structuralcomponent for machines, structural components for buildings, structuralcomponents for photovoltaic equipments or structural components formechanical devices.
 9. The article of claim 7 in the form of automotivepowertrain covers and housings, engine cover brackets, steering columnsframe, oil pans, and exhaust system components.
 10. A process for makingthe composite structure of claim 1, the process comprising the step of:impregnating the fibrous material under heat and pressure with thematrix resin wherein at least a portion of the surface of the compositestructure comprises the surface resin composition;
 11. The process ofclaim 10 wherein the matrix heat stabilizer is selected fromdipentaerythritol, tripentaerythritol, pentaerythritol and mixtures ofthese.